Process for recovering sugar from plant products containing the same



United States Patent 3,133,835 PRQCESS FGR RECOVERING SUGAR FRGM PLANT PRODUCTS (IQNTAENING THE SAME Walter Hermann Steclrel, 8 Riehlstrasse, Berlin-Charlottenburg 9, Germany Filed Nov. 13, 1961, Ser. No. 151,895 1 Claim. (Q1. 127-45) This invention peratins to a new and improved process for recovering sugar from plant products containing this material.

A large number of different processes are known for the recovery of sugar from sugar beets, sugarcane and the like. In general these processes fall into either of two difierent general categories. The first of these categories encompasses a large number of processes in which the cell structure of sugar containing plant material is disrupted to a substantial or material extent through the use of attrition mills or the like. The pulp obtained from such mills is generally treated on rolls, filters or the like so as to separate a sugar containing solution from an insoluble residue. The second of these general categories includes processes in which sugar containing material, such as sugar beets, is comminuted into chips or cossettes. These chips are then extracted with water so as to obtain a sugar solution and spent chips from which the sugar values have been largely removed.

It would be impossible to discuss virtually all aspects of the two general types of processes indicated above. Neither of them is considered completely satisfactory at the present time. When sugar is recovered by extraction of chips of a sugar carrying material a significant amount of the sugar remains in the individual chips or cossettes. This, of course, represents an economic loss. Further, with processes of this type a comparatively large amount of time is consumed and this leads to side effects of a disadvantageous character. These side effects are also found in processes of the first general type indicated in the preceding discussion.

In any process for the recovery of sugar from plant substance containing this material, it is desired to obtain a sugar solution of a relatively pure character. The word pure here is used in several different senses. It is desired to obtain a sugar solution which is substantially color free since the presence of color forming ingredients in such a solution will indicate the presence of unwanted material tending to contaminate the sugar itself. Further, it is desired to obtain a sugar solution which is substantially free from colloids since such colloids are impurities which must be removed prior to the sale of the sugar and since such impurities tend to interfere with purification steps. Thus, for example, they tend to clog up conventionally used filter media and the like. Further, it is desired to obtain a sugar solution that is pure in that it does not contain invert sugar, since such invert sugar is undesired for commercial reasons.

Any process for the recovery of sugar from plant substances, such as sugar beets, sugar cane or the like to be acceptable must not only produce a comparatively pure sugar solution as indicated above, but it must also be of such a character that the process does not require a large amount of water since the use of a comparatively large amount of water results in a comparatively dilute sugar solution being obtained. In other words, if too much water is used in the recovery of sugar, this water represents an economic loss since it must be gotten rid of in placing the sugar in a form in which it may be sold.

Any process for recovery of sugar to be acceptable at the present time must also provide the residue from which sugar has been obtained in a form in which it has significant economic value. It is well known that the spent cossettes or chips from one of the general types 3,133,835 Patented May 19, 1964 of processes indicated above can be used as cattle feed. It is also well known that the general type of process supplying such chips or cossettes is disadvantageous in many instances for reasons pertaining to the recovery of sugar.

The second general type of process indicated in the preceding discussion is also disadvantageous because of the problem of fines. Fine particles which can be loosely compared with common dust or the like tend to be produced in excess in the spent residue using prior process for the recovery of sugar in which the plant material is completely abraded or similarly broken up. Such fines are not generally considered acceptable as cattle feed in a commercial sense, although they may have at least a minimum of economic value as fuel and for other purposes.

A broad object of the present invention is to provide a new process for recovering sugar from plant products which constitutes a distinct commercial improvement over prior related processes as briefly discussed or indicated in the preceding. A related object of the present invention is to provide a process of this type which results in the production of a flake-like residue which is substantially free from fines or powdery material, and which, therefore, is very acceptable for use as cattle feed.

These and other objects of the invention, as well as many specific advantages of it will be fully apparent to those skilled in the art to which this invention pertains from a detailed consideration of the remainder of this description, including the appended claim and the accompanying drawing.

This drawing shows a flow sheet illustrating the process steps utilized in a preferred mode of carrying out this invention.

As an aid to understanding this invention it can be stated in essentially summary form that it concerns a process which involves the steps of breaking down sugar containing plant material into comparatively small fragments or particles and then subjecting these fragments to a series of mixing and separating steps during which the plant material is mixed with and then separated from water or recycled water containing sugar so as to obtain a final sugar solution, and a flake-like residue. These latter steps are carried out in a countercurrent manner so that fresh water is contacted with these particles immediately before they are passed from the process and then this water is recycled by gradual steps back to the initial mixing step so as to build up the sugar concentration Within it.

In the presently preferred manner of carrying out the process indicated in the above brief summary a mill 11 will be used to comminute about metric tons of plant material such as sugar beets at ambient temperature per 24 hour period. Preferably this mill 11 is set so that comminuted product produced by it consists of small particles of plant material in which the initial cell structure is substantially unaltered. The size of these particles is important. They should be as small as they can be made conveniently without breaking up the cell structures within their interior. The material from this mill 11 is conveyed directly into a mixer 12 which mixes it with recycled process solution, and then is conveyed to a continuous centrifuge 13. The continuous centrifuge 13 removes substantially pure sugar solution from the mixture conveyed to it from the mill l2, and produces a pulp containing of from about 10 to about 15 percent by weight of solid plant material. Preferably this centrifuge 13 is operated so as to produce a pulp containing about 12 percent by weight solids.

This pulp is directly conveyed from the centrifuge 13 to another mixer 14 which mixes with the pulp further recycled process solution and conveys the resulting slurry J) to a filter 15 where liquid is removed from it and where the filter cake is washed with further recycled process solution. The filter cake from the filter 15 is directly discharged to another mixer 16 which mixes it with recycled process solution so as to obtain a slurry which is passed to a final filter 17.

On this final filter 17 the filter cake is washed further with recycled process solution and then it is further washed with fresh water used as a source of water for the final sugar solution separated by the centrifuge 13. Normally fresh water is maintained at a temperature of from about 90 to 100 (3.; preferred results have been achieved by maintaining it at 92 C. Satisfactory results have been achieved using from about 20 to about 70 metric tons of fresh water, each 24 hour period per 100 tons of sugar containing plant material noted in the preceding. With sugar beets it is preferred to utilize from about 50 to about 70 metric tons fresh water per 100 tons sugar beats per 24 hour period.

The final filter 17 is preferably operated so that the filter cake on it is firmly compacted prior to removal from the filter media, and is removed from the filter media in the form of discrete, separate chips or flakes of from about 20 mm. by 30 mm. to about 20 mm. by 100 mm. in exterior dimensions and from about 3 /2 mm. to about 4 mm. thick having a solids content of from about 25% to about 28% by weight. These chips, in accordance with this invention, may be separately dried using conventional equipment such as a rotary drier so that they may be stored for a prolonged period prior to their use. They are distinguishable from prior related products inasmuch as the material within them is bonded as described subsequently in this specification so that they normally do not become comminuted into fines or powdery material during such drying.

The fresh water used in the process of this invention may be from any local source; as indicated in the drawing it is conveyed to the filter 1'7 through a pipe 19 so as to serve to wash the filter cake upon this filter 17 prior to its being discharged. The filtrate obtained from the fresh water conveyed through the pipe 19 is conveyed through a pipe 20 so that preferably about two-thirds of it is used as an initial wash water on the filter 17 and so that the remainder of it is added to the filter cake conveyed to the mixer 16.

The filtrate obtained on the filter 17 from the process fluid recycled through the pipe 20 is further recycled through a pipe 21 and is used as a final wash solution with respect to the filter cake on the filter 15 just prior to this filter cake being discharged from this filter. The process solution obtained as filtrate from the liquid conveyed from the pipe 21 is conveyed through the pipe 22 so that about two-thirds of it is used as the initial Wash for the filter cake on the filter 15 and so that the remainder of it is added to the material in the mixer 14. The initial filtrate obtained on the filter 15 consisting essentially of liquid conveyed through the pipe 12 is recycled through the pipe 23 to the mixer 12.

An exceedingly important factor in carrying out the process steps described is the amount of time consumed during the treatment of sugar containing plant material. Preferably all of the steps outlined in the preceding are carried out so that any specific plant material entering the mill 11 is discharged from the filter 17 within a time of from about 3 /2 to about 4 minutes. Further, the process is preferably carried out so that such plant material is in contact with ambient air no more than about one minute. As a consequence of this, the plant material treated in accordance with the process of this invention is held out of contact with ambient air to what is considered to be the maximum extent feasible.

Because temperature control is important in the process of this invention normally the temperatures of the recycled process solutions are held within the range of from about 90 to about 100 C., and preferably at about 92 to 94 C. in practicing this invention. Conventional heaters of an indirect type 25 may be used in order to heat the solution flowing through the pipes 20, 21, 22 and 23 in order to maintain temperatures within these ranges. At such temperatures efiicient, rapid extraction of sugar material from the plant material treated can be achieved. Further, by carrying out the steps as indicated substantially all the sugar values in such plant material are removed. In practicing the invention as herein described the filter cake discharged from the filter 17 normally contains no more than about 0.07 to about 0.2% by weight of the sugar in the plant material processed.

It is not normally preferred to store sugar solutions at elevated temperatures as indicated in the preceding because of the possibilities of bacterial degradation as well as other reactions. For this reason it is preferred to cool the sugar solution separated by the centrifuge 13 through the use of a conventional cooler 26 to about room temperature (about 20 C. or below), as soon as possible after such a solution is separated. The so-called solution may be processed in order to obtain purified granular sugar in accordance with known practice. it can also be used directly for certain purposes.

The equipment used in carrying out the present invention may be of a conventional type. The mill 11 is utilized is preferably of a type which comminutes plant material into comparatively small sized fragments as indicated without completely destroying or disrupting the cell structure of the material. Known attrition or hammer mills or various equipment such as equivalent mills having knives or cutting surfaces may be employed. Preferably the mixers 12, 14 and 16 are common screw conveyors although equivalents can be utilized. The filters 15 and 17 preferably are rotary drum filters such as Dorr type filters, although various equivalents such as rotary leaf filters or the like can be employed. If desired known continuous centrifuges may be substituted for the filters shown since, in many cases, this type of equipment may be operated so as to achieve the same results as are achieved on continuous filters. In order to implement this disclosure reference is made to the text Chemical Engineering Handbook by Perry, Fifth Edition, McGraw- Hill Book Company, New York, New York, copyright 1951 for reference to various known type of equipment as indicated in this discussion.

By carrying out the process of this invention as indicated in the preceding a number of distinct advantages are achieved. Initially the mill 11 comminutes plant material to comparatively small particles or fragments which are sufficiently small so that substantially all of the sugar within such particles or fragments can be removed from them by the simple procedure indicated in the preceding. Further, the mill 11 does not reduce such plant material to such a small size that the cell structure within it is completely disrupted. As a consequence of this various undesirable compounds within the plant material which might tend to form colloids upon leaching are held within the plant material during the steps in the process of this invention following the additional comminution. Such undesirable compounds in some cases will also tend to affect the color of the sugar solution obtained. In effect, in carrying out the process of this invention the plant material is never comminuted to a point where such undesired compounds are released from the cell structure within plant material to a substantial or material degree.

Further, as the process described in the preceding is carried out the duration of contact of liquid with the plant material is minimized so that no recycled liquor is in contact with any plant material for a period of more than a period of a few minutes. This has the effect of minimizing bacterial degradation of the plant material since significant amounts of bacterial growth are dependent upon prolonged contact with appropriate growth media at a temperature serving to promote such growth.

As a consequence of this any bacterial degradation which might tend to cause discoloration of the solution achieved or the formation of various colloids or the like is effectively minimized. Further, any tendency of bacteria to degrade sucrose to invert sugar is prevented for substantially the same reason.

A further significant advantage of the present invention lies in the fact that the process as described in the preceding effectively provides a chip-like residue which can be satisfactorily utilized as cattle feed. The chip-like character of this residue, as opposed to the fine particles of a dust-like character of residues from prior related processes for recovering sugar, is considered to be related to a satisfactory control of reactions of pectic substances Within the sugar containing plant material and to the efficient utilization of such pectic substances.

It is well known that pectic substances are primarily composed of polygalactuonic acid and various derivatives of it. It is also known that pectic polymers may be de-esterified by prolonged presence in solution with enzymes or the like such as are naturally present in sugar bearing plant material. Such de-esterfication tends to break up the molecular structure of pectic substances so as to yield degradation products of a colloidal character. By virtue of the limited time with which plant material is in contact with any specific quantity of process solution in carrying out the process of the present invention, and the relative small quantity of any process solution in contact with such plant material at any one time such degradation reactions are minimized to a maximum possible extent, even though the comparatively elevated temperatures utilized in practicing this invention tend to promote such reactions.

By virtue of the fact that degradation of pectic materials present within sugar-bearing plant material are held at minimum in practicing this invention an improvement in the filterability of these plant materials is noted. Such improvement of course contributes to the ease with which the process of the present invention may be carried out Without clogging filter media. It is believed that treatment of the pectic substances in plant material as set forth in the preceding is dmirable inasmuch as it causes a certain amount of swelling of these substances and facilitates the ability of these substances to act as binders for plant material during treatment upon a filter media forming a filter cake. In order to increase the binder action of such pectic substances on the final filter 17 it is possible to use a roller or similar compressing media serving to force water from the filter cake. This binder action achieved through the use of these pectic substances is considered to be sufiicient so as to prevent the plant material removed from the final filter from breaking up into fines during subsequent, conventional drying steps.

It is noted that the treatment of sugar bearing plant material in accordance with this invention is designed so as to not only effectively control bacterial action tending to destroy sugar and so as to not only effectively prevent the liberation of undesired compounds from such plant material, but is also intended so as to minimize losses as may result from various oxidation reactions. Such reactions are held to a minimum by virtue of the fact that the process herein described is carried out over a comparatively short period, and by virtue of the fact that various steps of this process, such as, for example, the mixing steps specified are preferably carried out in the absence of ambient air. As a consequence of the various factors indicated in this specification a sugar solution can be obtained from plant materials such as sugar beets, sugar cane or the like which is of a comparatively much lighter color than prior solutions of a similar character and which is substantially free from various unwanted sugar degradation products and various other types of undesired compounds or colloidal materials.

Those skilled in the art to Which this invention pertains will realize that the basic features of this invention can be applied in a number of different Ways With different types of equipment. They will also realize that advantages herein explained may be obtained using other than the specific number of mixing and separating steps indicated. Because of the nature of this invention it is to be consid ered as being limited only by the appended claim forming a part of this specification.

This application is a continuation-in-part of the copending application for U.S. Letters Patent Serial No. 476,842 filed December 21, 1954, and entitled Products of Fodder From Medullary Substances of Sugar, etc. The entire disclosure of this earlier filed co-pending application is incorporated herein by reference.

I claim:

A process for producing a sugar solution from sugar containing plant material, which process includes:

comminuting sugar containing plant material to small particles having substantially unaltered cell structures within their interiors and thereafter contacting said comminuted material with water at a temperature of from about to about C. during a series of successive mixing and separating operations carried out for a period of from about three and one half to about four minutes in a countercurrent manner with said comminuted material being initially mixed with recirculated water in the first of said operations and being passed therefrom through successive mixing and separating operations of said series and with said Water being initially added to the last mixing operation of said series and being separated from said material in the last separating operation of said series and being thereafter successively recirculated therefrom to the mixing operations of said series preceding the operation to which it had previously been added, said water being removed from said process after said initial separating operation in the form of a sugar solution, said last separating operation being carried out by filtration, the pectic materials with said solid material aiding in the formation of a filtercake and facilitating said filtration, said comminuted plant material being compressed during said last separating operation to a thickness of from about three and a half to about four mm. and being removed from said process following the last of said separating operations in the form of flakes, said flakes containing from about 25% to about 28% solid material and the balance water, said flakes being held together by a binder action of the pectic materials Within said solid material.

References Cited in the file of this patent UNITED STATES PATENTS 1,185,009 Searby May 30, 1916 1,617,962 Nobel Feb. 15, 1927 1,683,782 Johnson Sept. 11, 1928 1,688,905 Vazquez Oct. 23, 1928 2,273,557 Bonotto Feb. 17, 1942 FOREIGN PATENTS 27,666 Great Britain Dec. 1, 1904 of 1903 206,876 Australia Mar. 6, 1957 1,001,199 Germany Jan. 17, 1957 

